The present invention refers to a flame-resistant electric line consisting of at least one electric conductor, an insulation surrounding same, and a ribbon of glass cloth wrapped with overlapping edges around the insulated conductor and provided with a layer of metal on one side.
West German Pat. No. 30 44 871 provides this.
"Lines" within the meaning of the invention are intended to be lines by which communication engineering signals can be transmitted with low loss and free of interference. Thus in principle high-frequency (HF) lines and low-frequency (LF) lines are concerned. HF lines are used, for instance, in radio direction finding and antenna systems as well as in ultrashort wave broadcast and television receiving systems. LF lines are required, for instance, for electroacoustics and audio frequency measurements. With only one conductor they are used, for instance, as connecting wire for crystal microphones, magnetic sound heads and dictation machines.
For the development of the lines and for the materials used for this, fundamentally, only their electrical properties for the obtaining of the best transmission properties are taken into consideration. For many uses, such as, for instance, upon installation in buildings or switchboards, assurance must also be had that in case of fire and lines themselves will not burn and that they will continue to operate even at very high temperatures for at least a certain period of time. In this sense, by the expression "flame resistant" there are to be understood those special properties of an electric line in case of a fire which include freedom from smoke, non-burnability and freedom from halogens.
West German No. 05 28 00 688 describes an electric cable having conductors whose insulation consists of a mica ribbon with a layer of rubber lying over it. The insulated conductors (wires) of this cable are wrapped with an aluminum-plastic laminate. Around the cable core consisting of the wires, there is wrapped a polyester ribbon, over which a layer of a thermoplastic elastomer filled with aluminum hydroxide is applied. Above this there is wound a fiberglass mat over which a braided metal armoring is present. As outer protective sheathing, a layer of chlorosulfonated polyethylene is applied. The expense for the manufacture of such a cable is considerable. This is true both of the conductors, the insulation of which includes a mica ribbon, and of the entire cable, the sheathing of which surrounding the cable core consists of five different layers which cannot be applied in a single operation. Such a cable is therefore scarcely feasible economically.
The line of the aforementioned German Pat. No. 30 44 871 is of substantially simpler construction. In it only a single polyester ribbon coated with aluminum and an outer protective sheathing of plastic applied over the core, which is formed of a plurality of insulated conductors. A highly filled polyvinyl chloride mixture is used for the insulating of the conductors. The purpose hereof is to see to it that the insulation still remains stable even at very high temperatures of more than 1000.degree. C. so that short-circuits are avoided. Because of the special insulating material this known conductor cannot be used for cases in which there are high demands on the transmisstion properties. Furthermore should fire for any reason still reach the polyvinyl chloride, then the polyvinyl chloride itself begins to burn, liberating highly toxic and dangerous gaseous chlorine.
It is an object of the invention to provide a flame-resistant line which, while still of simple construction, satisfies high demands as to its transmission properties and is unburnable even at temperatures of more than 1000.degree. C.